Some jurisdictions are creating regulations allowing a radio, such as a cognitive radio (CR), to operate in certain frequency bands on a licensed-exempt basis (e.g., without requiring a license to broadcast on the frequency bands). For example, the Federal Communications Commission (FCC) has allocated the ultrahigh frequency (UHF) band (commonly used for UHF TV) for licensed-exempt use, and the vacant channels in this band are referred to as white space or TV white space (TVWS). Other jurisdictions around the world, such as Office of Communications (OFCOM) in the United Kingdom, are also making white space available. To that end, the Internet Engineering Task Force (IETF) is developing standards for protocols for accessing databases (see, for example, Protocol to Access White Space Database, draft-ietf-paws-protocol-03, February 2013, and other related and subsequent standards, hereinafter PAWS). Moreover, these databases may be certified by regulators, such as the FCC and the like, to operate in a given regulatory region or domain.
To use the TV white space, regulators typically mandate a lookup into a database containing available frequencies (e.g., also referred to as available channels and/or an available channel list) at a given location before a device can transmit in the given location. This lookup is typically required by regulators to prevent usage on the TV white space to interfere with licensed spectrum usage, such as licensed TV UHF broadcasts. Moreover, a master device is typically used to access the database and obtain the available frequencies and respective maximum permitted transmit powers for those frequencies. The master device knows its location and is authorized to receive from the database available frequencies based on location. The master device may then provide the available frequencies to associated white space devices (also referred to as slaves), so that the white space devices can transmit on the available frequencies.
The white space device may comprise a radio that is a so-called “slave” device because it may not know its location (even though it may have a location determination capability, this capability may not function or may be inoperative) or the slave does not have the necessary functionality to communicate to an authorized database configured to provide available frequencies. Instead, the slave relies on the master device to obtain available frequency/channel information obtained from the database. For example, the white space device (or slave) may check for available frequencies by requesting the available frequencies from the master device serving the slave. Next, the master provides to the database a request for available frequencies and location information (representative of the location of the master device). The database returns to the master the available white space frequencies and optionally maximum transmit powers for the given location. Next, the master delivers the available frequencies and/or maximum transmit powers to the slave. The slave device may then operate on any of the available frequencies provided by the master, so long as the slave remains within range of the master. In the case of the FCC, the slave may use the available frequencies provided by the master, so long as the slave receives a contact verification signal (CVS) transmitted by the master device.